1. Field of the Invention
The invention relates to a method and apparatus for machining workpieces, and more particularly, a method and apparatus for accurately and simply creating complex bodies from primitives wherein tool corrections have been incorporated.
2. Description of the Prior Art
In numerically controlled (NC) machine tools, data for producing a workpiece from a workpiece blank is derived in the form of tool path data by means of an NC program. The tool path data produces a tool path contour which differs from the desired contour of the workpiece. The difference is due to the tool radius. More specifically, the NC machine operates the tool based upon the center point of the tool path contour. When the tool is moved along the tool path contour, the actual cutting, drilling or other operation performed by the tool occurs at a certain distance from the tool path contour, namely the tool radius. Thus, if a workpiece having the desired workpiece contour is to be created, the tool must be moved according to the tool path contour. The tool path contour will often be referred to as the corrected contour throughout the remainder of the specification.
Often, the workpiece to be produced by the NC machine is a complex body formed by various shapes. It is often difficult to define such a complex body and determine the intersection line contour or workpiece contour between the workpiece and an applicable machining plane. In addition, correcting the workpiece contour for the tool radius so that a particular tool will create the desired workpiece, taking into account possible collisions with a given accuracy, is a complex task requiring a great deal of calculation. The amount of computer capacity and memory capacity needed is thus correspondingly high. To perform such calculations, additional hardware and software are necessary on the NC control computer. These include special arithmetic processors, for instance, as well as geometric methods and display methods for describing free-form surfaces.
It is known that workpieces having complex shapes can often be created by combining primitives such as cylinders, rectangles and spheres using set theory operations. In addition, relatively complex body contours can be put together from simple contour parts such as circles and rectilinear lines. The tool radius corrections can be carried out easily with these simple contours. It is problematic, however, to ascertain the resultant tool path from the various corrected contours, since overlapping occurs when the various corrected contours are put together. For instance, U.S. Pat. No. 4,868,761 (Hayashi), which corresponds to German Published, Non-Examined Patent Application 36 08 438, discloses a method of calculating free, curved edges for manufacture by means of numerically controlled machines by means of computer-aided design (CAD) and computer-aided manufacture (CAM). In addition, set theory, also known as Boolean operation, is used to combine simple mathematically definable bodies to form a complex body. The function of defining a shape, however, is completely separate from the function of determining the geometric location of a tool. The latter is the task of numerical control.
An object of the present invention is to provide a method and apparatus of machining workpieces in a simple manner.
A further object of the present invention provides a method and apparatus for ascertaining tool path contours that produce a workpiece having desired workpiece contours.
Further objects and advantages will become apparent from the following description and the accompanying drawings.